This invention relates to photopolymerizable (i.e. photohardenable) compositions. More particularly, this invention relates to complex salt photoinitiators useful in such compositions.
One-part photocurable epoxide compositions containing a diaryliodonium complex salt photoinitiator have been previously described. One-part photocurable compositions containing a triarylsulfonium complex salt photoinitiator have also been previously described (e.g. in assignee's copending applications Ser. Nos. 609,897 and 609,898, filed Sept. 2, 1975, and in U.S. Pat. No. 4,069,054, all incorporated herein by reference). Such compositions have commercial utility for many applications such as protective coatings for wood, metal, paperboard, floor tile, lithographic printing plates, printing inks, circuit board solder masks, etc. Such protective coatings are typically thin films of about 0.1 to 3 mils (e.g. 0.002 to 0.08 millimeters) that rapidly photocure when exposed to light.
The above-described compositions are 100% solids (i.e. they do not contain volatile non-reactive solvents). Consequently, such compositions are of major importance in eliminating air pollution and gas drying ovens which are very energy-consumptive.
There are many potential applications for curable compositions in the form of thick films or coatings, e.g. encapsulation of electronic components, reinforced plastics, relief printing plates, autobody repair, and sealants. In such applications the composition must be capable of curing rapidly to thicknesses up to one-half inch (approximately 1.3 centimeters) or more. The photocurable compositions described hereinbefore have not been known to exhibit such thick cure capability.